Immunoassay. Innovations in label technology

The history and recent developments in label technology are reviewed. Because the new labels generally are used in both classic immunoassays and immunometric assays, a brief review of the advantages and disadvantages of each type of assay is included. Recent developments in enzyme labels, such as channeling techniques, enzyme acceptor-donor systems, and apoenzyme reactivation assays, are discussed. Fluorescence polarization immunoassay and time-resolved fluorescence using the lanthanides are two of the newer fluorescence techniques. Luminescent labels, such as acridinium esters, show promise because of their stability, sensitivity, and ease of detection. Several new particle label techniques have been introduced, perhaps two of the most interesting of which are sol particle and liposome labels. Advantages and disadvantages of the newer labels are compared with those of radioactivity.